The present invention relates generally to peak detectors and more particularly to a peak detector for a small input signal.
In disks, such as DVD or DVD-RAM, information is recorded in sector units. A sector includes a header information area having a physical identification data and a user data area. The header information area is typically divided into a peak header area and a bottom header area, and user data is divided into land area and groove area. In DVD-RAM disks, a track is formed spirally, and the track is shifted laterally at a predetermined reference point. The reference point usually becomes a starting point of the first sector.
In DVD applications, peak detectors are used. An AC peak detector is non-linear circuit used to obtain a steady state amplitude at a level of the peak amplitude of the input AC signal. The input AC signal need not be a uniform sinusoidal or an infinite sum of sinusoidals such as in a square wave signal, but any signal with approximately complimentary positive and negative voltage peaks, such as communication data signal can be an AC signal.
A number of peak detector designs are known, however, each design has shortcomings which limit the range of operability and performance within that range. In particular, there is a need for peak detectors which detect peaks with amplitudes as low as 50 or even 20 millivolts. The known designs do not demonstrate acceptable performance at such levels and more particularly has dead zones where a new peak is not recorded.
FIG. 1 illustrates a peak hold circuit. An input signal is input to the base of transistor 100. A current flows from collector to base of collector 100. If the current exceeds the current flowing in the constant current source 102, current flows through capacitor 104 and charges up capacitor 104. The voltage on capacitor 104 is the peak hold voltage.
FIG. 2 illustrates a typical input voltage. As discussed before, the input signal need not be sinusoidal. FIGS. 2 and 3 illustrates wave forms including the held voltage at the top of the wave form.
FIG. 3 illustrates the relationship between the input amplitude and the peak hold voltage and the input amplitude. As can be very clearly seen, this circuit introduces a large amount of dead region that is not representative of the peak voltage.
The present invention provides a peak hold circuit that includes a track and hold circuit and a comparator circuit which provide improved peak detection with minimal dead regions.